Rosin - Rammler model (1933) is the Weibull distribution which was proposed by Weibull in 1939, and Weibull distribution functions are part of R.
So the user can use stats::dweibull(x,shape=ex,scale=xs) the same way as drr,
and use Weibull distribution functions provided by stats package for deeper analysis.
Similarly, stats::pweibull(x,shape=ex,scale=xs) can be used the same way as urr orstats::pweibull(x,shape=ex,scale=xs,lower.tail=F) the same way as orr.